JP7681575B2 - Thermochromic writing implements - Google Patents

Description

The present invention relates to a writing instrument. More specifically, the present invention relates to a writing instrument equipped with a friction body for thermally discoloring handwriting made of thermochromic ink.

In recent years, thermochromic writing instruments have become widespread. Thermochromic writing instruments contain thermochromic ink. The mark made with thermochromic ink can be discolored or erased by heating. Thermochromic writing instruments are equipped with a friction body that generates frictional heat to erase or discolor the mark made with thermochromic ink. Note that "discoloration" of thermochromic ink means changing from one color to another color. "Discoloration" is one form of discoloration, and means changing from one color to colorless.

For example, WO 2018/116767 discloses a writing instrument with a thermochromic ink containing a metallic luster pigment added to the thermochromic ink. This thermochromic writing instrument is equipped with a friction body containing a viscoelastic body. This friction body is capable of chemically and physically erasing the thermochromic ink containing the metallic luster pigment. That is, the friction body containing a viscoelastic body erases the thermochromic ink by frictional heat, and adsorbs the metallic luster pigment by viscoelasticity and peels it off from the paper surface. In this way, the friction body containing a viscoelastic body disclosed in WO 2018/116767 has both chemical erasability that erases the thermochromic ink by frictional heat and physical erasability that peels off the metallic luster pigment by viscoelasticity.

International Publication No. 2018/116767

However, a problem with friction bodies that contain viscoelastic bodies is that the amount of deformation of the friction body gradually increases due to the reciprocating motion (hereinafter referred to as "frictional action") when rubbing the handwriting of thermochromic ink. In other words, a viscoelastic body has the property that the amount of deformation increases over time when a certain external force is applied. For this reason, friction bodies that contain viscoelastic bodies gradually become more deformed by repeated frictional action. When the amount of deformation of the friction body becomes large, it may not be possible to generate the frictional heat required to discolor or erase the handwriting of thermochromic ink.

On the other hand, if the force for frictionally operating the friction body is gradually reduced, the amount of deformation of the friction body can be kept constant. However, there are cases where the force for frictionally operating the friction body is too small to generate the frictional heat required to discolor or erase the written mark of thermochromic ink. In particular, the elastic modulus of a friction body made of synthetic resin depends on temperature. For this reason, when the temperature of the friction body itself rises due to frictional heat, and when the friction body is used in a high-temperature environment, the friction body is more likely to deform significantly.

The present invention has been made to solve the above-mentioned problems, and aims to provide a thermochromic writing instrument that makes it possible to chemically and physically erase traces of thermochromic ink containing added metallic luster pigments, and that can cause the friction body to exhibit the desired friction performance by suppressing deformation of the friction body.

(1) In order to achieve the above object, the thermochromic writing instrument of the present invention is a thermochromic writing instrument comprising a thermochromic ink and a friction body for thermally discoloring a mark written with the thermochromic ink by frictional heat, wherein a metallic luster pigment is added to the thermochromic ink, the thermochromic writing instrument is provided with a mounting hole for mounting the friction body, the friction body includes a mounting portion to be inserted into the mounting hole and a friction portion having a convex curved shape protruding from the mounting hole, a volume Ve of the friction portion and a volume Vp of the metallic luster pigment satisfy 5≦Ve/Vp≦35, a maximum outer diameter D and a protruding length L of the friction portion satisfy 0.1≦L/D≦1.5, and the material of the friction body satisfies JIS K The Shore A hardness measured in accordance with JIS H7215 immediately after the start of contact with the indenter is in the range of 60 to 85, and the Shore A hardness (ΔHS) defined by the following formula is 0 to less than 5.
ΔHS=(Shore A hardness value immediately after the indenter starts contacting)−(Shore A hardness value 15 seconds after the indenter starts contacting)

The friction body provided in the thermochromic writing instrument of (1) above can chemically discolor or decolorize the handwriting of the thermochromic ink by frictional heat, and can also physically peel off the metallic luster pigment added to the thermochromic ink. On the other hand, by making the ΔHS of the material of the friction body less than 5, it is possible to give the friction part sufficient rigidity against frictional action. This suppresses deformation of the friction part when subjected to frictional action, allowing the friction part to exhibit the desired frictional performance.

(2) Preferably, in the thermochromic writing instrument of (1) above, the material of the friction body has a product (Tb x Eb) of the tensile strength at break Tb and the elongation at break Eb, measured in accordance with JIS K 6251 of the Japanese Industrial Standards, of 5,000 or more and 18,000 or less.

By setting the product of the tensile strength at break Tb and the elongation at break Eb (Tb x Eb) of the friction body material to between 5,000 and 18,000, the friction body generates an appropriate amount of wear debris when rubbing handwriting. This allows the metallic luster pigment added to the thermochromic ink to adhere to and be wrapped around the wear debris.

(3) Preferably, in the thermochromic writing instrument of (1) or (2) above, the mounting hole is provided so as to penetrate the rear end of the barrel or the top of the cap constituting the thermochromic writing instrument along the vertical central axis, has an inner circumferential surface between two openings located at the upper and lower ends, an inward protrusion protruding toward the inside of the mounting hole is formed on the inner circumferential surface of the mounting hole, an outward protrusion protruding toward the outside of the mounting portion is formed on the outer circumferential surface of the mounting portion, and when the mounting portion is inserted into the mounting hole, the outward protrusion rides over the inward protrusion, thereby forming a front end. The outward protrusion and the inward protrusion are engaged with each other, the friction body has a straight inner hole along a vertical central axis that opens at least at the lower end of the mounting portion, and a rod-shaped core having a length that fits into the inner hole and an outer peripheral surface that contacts the inner peripheral surface of the inner hole is inserted into the inner hole, and when the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the core is held in a position corresponding to the inner peripheral surface of the mounting hole, so that the mounting portion is sandwiched between the outer peripheral surface of the core and the inward protrusion of the mounting hole.

The mounting portion of the friction body is sandwiched between the outer peripheral surface of the core and the inward protrusion of the mounting hole, and is firmly fixed to the mounting hole. This increases the rigidity of the entire friction portion, suppresses deformation of the friction portion when frictionally operated, and enables the friction portion to exhibit the desired friction performance. In particular, even if the friction portion is made of a material with low hardness, the entire friction portion can be given the desired rigidity. This allows the handwriting of the thermochromic ink to be thermochromic efficiently. Furthermore, the core is inserted into the inner hole of the friction body after the inward protrusion of the mounting hole and the outward protrusion of the mounting portion are engaged. This allows the friction body to be easily attached to the thermochromic writing instrument without requiring a large force.

(4) Preferably, in the thermochromic writing instrument of (3) above, when the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the core has a length from the opening at the lower end of the inner hole to the opening at the upper end of the mounting hole.

Because the core has a length from the lower opening of the inner hole to the upper opening of the mounting hole, if the friction portion wears out, the core will not become exposed from the friction portion and damage the paper surface.

(5) Preferably, in the thermochromic writing instrument of (3) or (4) above, when the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the lower end of the core is positioned at the same position as the lower end of the mounting portion or higher than the lower end of the mounting portion.

By positioning the lower end of the core at the same position as the lower end of the mounting part or higher than the lower end of the mounting part, it becomes easier to insert the core into the friction body, improving assembly.

(6) Preferably, in any of the thermochromic writing instruments (3) to (5) above, the inner hole is a hole that opens at the lower end of the attachment portion and is blocked on one side, i.e., does not open at the upper end of the friction portion, and a ventilation portion is provided in the core to exhaust air from within the inner hole during the process of inserting the core into the inner hole.

During the process of inserting the core into the inner hole, the air in the inner hole is not compressed by the core and is expelled to the outside. This makes it easier to insert the core into the friction body and ensures that the core is securely attached to the inner hole.

(7) Preferably, in the thermochromic writing instrument of (6) above, the ventilation portion is a through hole that penetrates from one end of the core to the other along the vertical central axis of the core.

During the process of inserting the core into the inner hole, the air in the inner hole is not compressed by the core and is reliably discharged to the outside through the through hole. This makes it easier to insert the core into the friction body and ensures that the core is securely attached to the inner hole.

(8) Preferably, in the thermochromic writing instrument of (6) above, the ventilation portion is at least one groove or protrusion that runs from one end of the core to the other along the outer peripheral surface of the core.

In the process of inserting the core into the inner hole, the grooves or protrusions of the core form a gap between the outer peripheral surface of the core and the inner peripheral surface of the inner hole. This ensures that the air in the inner hole is not compressed by the core and is reliably discharged to the outside through the gaps formed by the grooves or protrusions. This makes it easy to insert the core into the friction body and ensures that the core can be securely attached to the inner hole.

(9) Preferably, in any of the thermochromic writing instruments (3) to (8) above, the center core has a symmetrical shape in the vertical direction.

Because the core is symmetrical in the vertical direction, there is no distinction between the top and bottom of the core. This means that the core can be inserted into the inner hole from either the top or bottom, making it easier to insert the core into the inner hole.

(10) In the thermochromic writing instrument of any one of (3) to (9) above, preferably, a protrusion is provided on the outer circumferential surface of the center core, the protrusion contacting the inner circumferential surface of the inner hole .

The protrusions on the outer periphery of the core hold the core more firmly within the inner hole, thereby reliably preventing the core from falling out of the inner hole.

(11) In order to achieve the above object, the thermochromic writing instrument of the present invention is a thermochromic writing instrument comprising a thermochromic ink and a friction body for thermally discoloring writing marks made with the thermochromic ink by frictional heat, wherein the thermochromic ink is added with at least one of a fluorescent pigment, a phosphorescent pigment and titanium dioxide, the thermochromic writing instrument is provided with a mounting hole for attaching the friction body, the friction body includes a mounting portion that is inserted into the mounting hole and a friction portion having a convex curved shape that protrudes from the mounting hole, and the material of the friction body has a product (Tb x Eb) of the tensile strength at break Tb and the elongation at break Eb measured in accordance with JIS K 6251 of the Japanese Industrial Standards, of 5,000 or more and 18,000 or less.

By setting the product of the tensile strength at break Tb and the elongation at break Eb (Tb x Eb) of the material of the friction body to be between 5,000 and 18,000, the friction body generates an appropriate amount of wear debris when rubbing handwriting. This makes it possible for at least one of the fluorescent pigment, phosphorescent pigment, and titanium dioxide added to the thermochromic ink to adhere to and encase the wear debris.

The thermochromic writing instrument of the present invention makes it possible to chemically and physically erase handwriting made with thermochromic ink containing added metallic luster pigments, and by suppressing deformation of the friction body, it is possible to allow the friction body to exhibit the desired friction performance.

Here, in this specification, "front" of a thermochromic writing instrument means the direction of the pen tip, and "rear" of a thermochromic writing instrument means the direction opposite to the pen tip. Furthermore, "up" of a mounting hole means the direction of the rear end of the barrel or the direction of the top of the cap, and "down" of a mounting hole means the opposite direction. Furthermore, "up" of a friction body means the direction of the friction part, and "down" of a friction body means the direction of the mounting part. In addition, the content of multiple components constituting the composition described in this specification means the total amount of the substance corresponding to each component, unless otherwise specified. In addition, the term "metallic luster pigment" broadly includes pigments that can impart brilliance to the writing of a thermochromic ink. For example, both transparent metallic luster pigments and metal vapor deposition resin pigments are included in the term "metallic luster pigment".

FIG. 1 is a cross-sectional view showing a main part of a thermochromic writing instrument according to a first embodiment of the present invention, showing a state before an attachment part of a friction body is inserted into an attachment hole of a barrel. 10 is a cross-sectional view showing a temporary insertion state during the process of inserting the mounting portion of the friction body into the mounting hole of the barrel. FIG. 11 is a cross-sectional view showing a state in which the mounting portion of the friction body is inserted into the mounting hole of the barrel. FIG. FIG. 4 is a cross-sectional view showing a state in which a core is inserted into an inner hole of a friction body. FIG. 4 is a cross-sectional view showing a thermochromic writing instrument according to a second embodiment of the present invention. FIG. 11 is an external view showing a writing set including a thermochromic writing instrument and a friction body according to a third embodiment of the present invention.

Below, the thermochromic writing instrument relating to an embodiment of the present invention is described with reference to the drawings.

1. Overview Figures 1 to 4 show the main parts of a thermochromic writing instrument according to a first embodiment of the present invention. In Figures 1 to 4, the entire thermochromic writing instrument is not shown, and only the rear end of a barrel 1 constituting the thermochromic writing instrument is shown. The thermochromic writing instrument of this embodiment comprises a barrel 1, a friction body 3, and a core 7. An attachment hole 2 is provided at the rear end of the barrel 1. The friction body 3 is attached to the attachment hole 2. The friction body 3 is provided with an inner hole 31 along the vertical central axis. The core 7 is inserted into the inner hole 31.

2. Mounting Hole As shown in FIG. 1, a mounting hole 2 is provided at the rear end of the barrel 1. The mounting hole 2 penetrates the rear end of the barrel 1 along the vertical central axis. The mounting hole 2 has an inner circumferential surface between two openings located at the upper and lower ends. An annular inward protrusion 21 is formed below the inner circumferential surface of the mounting hole 2. The inner circumferential surface of the inward protrusion 21 is formed with a guide surface 21a, which is an inverted cone-shaped tapered surface. The diameter of the guide surface 21a gradually decreases from top to bottom. The lower end of the guide surface 21a is continuous with the vertical inner circumferential surface of the minimum diameter portion 21b, which is the opening at the lower end of the mounting hole 2. The horizontal cross-sectional shape of such a mounting hole 2 is a circle with a different diameter.

Here, the barrel 1 is manufactured by injection molding a synthetic resin (e.g., polypropylene). The mounting hole 2 and the inward projection 21 are integrally molded into the rear end of the barrel 1 by injection molding. Note that the mounting hole 2 is not limited to the rear end of the barrel 1, and may be provided, for example, at the top of a cap that constitutes a thermochromic writing instrument.

3. Friction Body As shown in Fig. 1, the friction body 3 of this embodiment is configured such that an attachment part 5 (small diameter part) having a smaller diameter than the friction part 32 is integrally molded below a bullet-shaped friction part 32 (large diameter part 4). The friction part 32 is used to cause the thermochromic ink attached to the paper surface to thermally discolor by frictional heat. Furthermore, the friction part 32 of this embodiment has the function of adsorbing and peeling off the metallic luster pigment added to the thermochromic ink from the paper surface. The attachment part 5 is used to attach the friction body 3 to the attachment hole 2 of the barrel 1.

3.1 Friction part (large diameter part)
The outer peripheral surface of the friction portion 32 has a convex curved shape that can contact the paper surface at various inclination angles. The diameter of the lower end of the friction portion 32 is larger than the diameter of the opening at the upper end of the mounting hole 2, and is preferably smaller than the diameter of the rear end face of the barrel 1. An annular surface 41 that abuts against the rear end face of the barrel 1 is formed at the boundary between the friction portion 32 and the mounting portion 5. When the mounting portion 5 is attached to the mounting hole 2, the friction portion 32 protrudes upward beyond the rear end face of the barrel 1.

1, the maximum outer diameter D of the friction portion 32 and the projection length L of the friction portion 32 satisfy 0.1≦L/D≦1.5, and preferably satisfy 0.5≦L/D≦1.1. The ratio L/D of the maximum outer diameter D and the projection length L of the friction portion 32 is an indication of the size of the portion of the friction portion 32 exposed to the outside and the rigidity of the friction portion 32. When the value of L/D is 0.1 or more, the friction portion 32 has sufficient rigidity to rub the handwriting on the paper surface. On the other hand, when the value of L/D is 1.5 or less, the friction portion 32 has an exposed portion large enough to erase many handwritings. The friction portion 32 of this embodiment has a maximum outer diameter D = 6.1, a projection length L = 6.3, and L/D ≒ 1.0.

When the friction portion 32 has a convex curved shape, it is preferable to make the thickness of the apex of the friction portion 32 the thickest. This increases the rigidity of the apex and the area near the apex, which is used when rubbing the handwriting on the paper, and allows for smooth frictional action.

3.2 Mounting portion The mounting portion 5 is made of a cylindrical wall portion, and has a diameter smaller than the diameter of the lower end of the friction portion 32 and capable of being inserted into the mounting hole 2. An annular outward protrusion 51 is formed in the center of the outer circumferential surface of the mounting portion 5. An annular bulge 52 is formed above the outward protrusion 51 on the outer circumferential surface of the mounting portion 5. Below the outward protrusion 51 on the mounting portion 5, a cylindrical portion 53 is formed.

A guide surface 51a, which is an inverted cone-shaped tapered surface, is formed on the outer peripheral surface of the outward protrusion 51. The diameter of the guide surface 51a gradually increases from bottom to top. The upper end of the guide surface 51a is continuous with the vertical outer peripheral surface of the maximum outer diameter portion 51b of the outward protrusion 51. The upper end of the vertical outer peripheral surface of the maximum outer diameter portion 51b is continuous with a horizontal annular upper end surface.

Here, the diameter of the maximum outer diameter portion 51b of the outward projection 51 is larger than the diameter of the minimum inner diameter portion 21b of the inward projection 21 of the mounting hole 2 described above, and smaller than the diameter of the opening at the upper end of the mounting hole 2. For example, the dimensional difference between the maximum outer diameter portion 51b and the minimum inner diameter portion 21b is within the range of 0.5 mm to 2.0 mm, preferably within the range of 0.5 mm to 1.0 mm. Due to such a dimensional difference, when the mounting part 5 is inserted into the mounting hole 2, the outward projection 51 passes smoothly through the inward projection 21, making it possible to easily engage the outward projection 51 and the inward projection 21 (see Figures 2 and 3).

When the mounting portion 5 is fully inserted into the mounting hole 2, the bulge portion 52 comes into contact with the inner circumferential surface of the opening at the upper end of the mounting hole 2 (see FIG. 3). This suppresses radial wobble of the friction body 3. The diameter of the bulge portion 52 is approximately the same as the diameter of the opening at the upper end of the mounting hole 2. The diameter of the bulge portion 52 is also smaller than the diameter of the lower end of the friction portion 32 and larger than the diameter of the maximum outer diameter portion 51b of the outward protrusion 51.

The diameter of the cylindrical portion 53 is smaller than the diameter of the minimum inner diameter portion 21b of the inward protrusion 21 of the mounting hole 2 described above. The cylindrical portion 53 is for putting the mounting portion 5 into a temporary insertion state into the mounting hole 2. This temporary insertion state is shown in FIG. 2. Such a cylindrical portion 53 makes it easier to install the friction body 3. That is, the friction body 3 can be dropped toward the mounting hole 2 to put it into the temporary insertion state shown in FIG. 2. Then, by pushing the friction body 3 toward the mounting hole 2, the mounting portion 5 is completely inserted into the mounting hole 2, and at the same time, the outward protrusion 51 and the inward protrusion 21 are engaged (see FIG. 3). Note that the outer peripheral surface below the outward protrusion 51 in the mounting portion 5 is not limited to the circumferential surface of the cylindrical portion 53, and may be, for example, an inverted cone-shaped tapered surface.

3.3 Formation of annular space The outer diameter of the middle part of the mounting part 5 (part between the bulging part 52 and the outward protrusion 51) is smaller than the inner diameter of the vicinity of the entrance of the mounting hole 2 (part above the inward protrusion 21). As a result, in the temporary insertion state shown in FIG. 2, an annular space 6 is formed between the mounting part 5 and the mounting hole 2. Due to this annular space 6, the middle part of the mounting part 5 is not pressed against the inner circumferential surface near the entrance of the mounting hole 2. That is, after the temporary insertion state shown in FIG. 2, the outward protrusion 51 of the mounting part 5 rides over the inward protrusion 21 of the mounting hole 2. At this time, the outward protrusion 51 is strongly pressed against the inward protrusion 21, so that the middle part of the mounting part 5 is elastically deformed and bulges outward in the radial direction. If the middle part of the mounting part 5 is pressed against the inner circumferential surface near the entrance of the mounting hole 2, frictional resistance that prevents the mounting part 5 from being inserted will be generated. The annular space 6 accommodates the intermediate portion of the mounting portion 5 which bulges radially outward, thereby preventing the intermediate portion of the mounting portion 5 from being pressed against the inner circumferential surface near the entrance of the mounting hole 2 .

3.4 Axial clearance As shown in FIG. 1, the length A from the upper end of the mounting portion 5 to the upper end of the outward projection 51 is slightly larger than the length B from the upper end of the mounting hole 2 to the lower end of the inward projection 21. This ensures that the entire outward projection 51 passes through the inward projection 21. In other words, if the lengths A and B were the same, the upper end surface of the maximum outer diameter portion 51b of the outward projection 51 may not be able to pass through the inward projection 21 due to frictional resistance generated between the outward projection 51 and the inward projection 21. By making the length A of the mounting portion 5 slightly larger than the length B of the mounting hole 2, the entire outward projection 51 can pass through the inward projection 21 even after the annular surface 41 of the large diameter portion 4 abuts against the rear end of the barrel 1. This ensures that the entire outward projection 51 passes through the inward projection 21 even if frictional resistance occurs between the outward projection 51 and the inward projection 21. Here, the difference between the lengths A and B appears as a clearance C between the outward projection 51 and the inward projection 21 shown in Fig. 3. The clearance C is preferably in the range of 0.05 mm to 1.0 mm, and more preferably in the range of 0.1 mm to 0.5 mm. With such a small clearance C, the friction body 3 does not move in the direction of the central axis, and the engagement between the outward projection 51 and the inward projection 21 does not loosen.

3.5 Inner Hole An inner hole 31 is provided inside the friction body 3. The inner hole 31 is a straight hole provided along the central axis of the friction body 3, and opens at least at the lower end of the friction body 3. In this embodiment, the inner hole 31 is a hole that extends from the lower end of the attachment portion 5 to the center of the friction portion 32, and is closed on one side, not opening at the upper end of the friction portion 32. The inner hole 31 is provided from the lower end of the attachment portion 5 to a position that reaches at least the upper end of the outward protrusion 51. Such an inner hole 31 makes it easier for the outward protrusion 51 to deform radially inward. This makes it easy to engage the outward protrusion 51 and the inward protrusion 21. Furthermore, a center core 7, which will be described later, is inserted into the inner hole 31.

Here, the inner hole 31 in this embodiment opens at the lower end of the attachment portion 5 of the friction body 3, and does not open at the upper end of the friction portion 32. If the inner hole 31 were to open at the upper end of the friction portion 32, it would not be possible to rub the handwriting at the upper end of the friction portion 32, and the friction performance of the friction portion 32 would be reduced.

In addition, since the inner hole 31 does not open at the upper end of the friction portion 32, the rigidity of the friction portion 32 is increased, improving the friction performance of the friction portion 32. Furthermore, when the friction body 3 is attached to the attachment hole 5, the entire friction body 3 is prevented from bending, making the attachment work easier.

3.6 Hardness and Viscosity of Friction Body The material constituting the friction body 3 is preferably a synthetic resin having elasticity (rubber, elastomer), and examples thereof include silicone resin, SBS resin (styrene-butadiene-styrene copolymer), SEBS resin (styrene-ethylene-butylene-styrene copolymer), fluorine-based resin, chloroprene resin, nitrile resin, polyester-based resin, ethylene propylene diene rubber (EPDM), etc.

Here, the friction body 3 of this embodiment has a lower hardness than conventional friction bodies in order to physically erase the metallic luster pigment added to the thermochromic ink described below from the paper surface. The friction body 3 with low hardness can penetrate into the depressions of the handwriting formed on the paper surface.

The hardness of the material of the friction body 3 is represented by the Shore A hardness value measured in accordance with the "Durometer hardness test method for plastics" specified in the Japanese Industrial Standards JIS K 7215-1986. The durometer used to measure the Shore A hardness value has a spring-loaded indenter, and the amount of indenter pressure on the object being measured is displayed as the Shore A hardness value. The softer the object being measured, the smaller the Shore A hardness value, and the harder the object being measured, the larger the Shore A hardness value.

It is preferable that the Shore A hardness value of the material of the friction body 3, measured by a test method in accordance with JIS K 7215-1986, satisfies the following conditions i) and ii).
i) The Shore A hardness value immediately after the initiation of contact with the indenter is 60 or more and 85 or less.
ii) The value of ΔHS defined by the following formula is 0 or more and less than 5.
ΔHS=(Shore A hardness value immediately after the indenter starts contacting)−(Shore A hardness value 15 seconds after the indenter starts contacting)
In the above i) and ii), "immediately after the indenter starts to come into contact" means within one second after the indenter comes into contact with the object to be measured.

The Shore A hardness value immediately after the initiation of the indentation contact in i) above is preferably 60 to 80, more preferably 65 to 75. The friction body 3 made of a material that satisfies the above condition i) has a higher frictional heat generation efficiency than conventional friction bodies. As a result, the friction body 3 can easily cause the handwriting of thermochromic ink to thermally discolor. In addition, the friction body 3 made of a material that satisfies the above condition i) is softer than conventional friction bodies and can penetrate into the depressions of the handwriting formed on the paper surface. Furthermore, by the material of the friction body 3 satisfying the ΔHS value in ii) above, it becomes possible to adsorb and peel off the metallic luster pigment from within the depressions of the handwriting.

The value of ΔHS in ii) above indicates the relaxation time of stress relaxation (change in stress over time) when a certain strain is applied to the material of the friction body 3. The time of stress relaxation is a criterion for distinguishing whether a material is an elastic body, a viscoelastic body, or a viscous body. A material of the friction body 3 that satisfies the value of ΔHS in ii) above can be said to be an elastic body with a moderate viscosity that enables it to adsorb metallic luster pigments. On the other hand, a material with a ΔHS value of 5 or more can be said to be a viscous body or a viscoelastic body. If the friction body 3 is a viscous body or a viscoelastic body, the amount of deformation when the handwriting of the thermochromic ink is rubbed becomes too large, and sufficient friction performance cannot be obtained. In particular, the elastic modulus of the friction body 3 made of synthetic resin depends on temperature. For this reason, when the temperature of the friction body 3 itself rises due to frictional heat, and when the friction body 3 is used in a high-temperature environment, the friction body 3 is more likely to deform significantly. Therefore, it is preferable that the ΔHS value of the material of the friction body 3 is 0 or more and less than 5. Here, the value of ΔHS in ii) above can be set arbitrarily depending on the type and/or composition of one or more comonomers contained in the polymer material.

The Shore A hardness values in i) and ii) above may be obtained by converting the Shore D hardness value of the material of the friction body 3 measured by a test method conforming to JIS K 7215-1986 into a Shore A hardness value.

3.7 Amount of wear of friction body In order to physically erase the metallic pigment added to the thermochromic ink from the paper surface, the friction body 3 is preferably one that is scraped off by rubbing the paper surface and generates a small amount of wear debris (eraser debris). The friction body 3 removes the metallic pigment from the paper surface by adhering it to the wear debris and enveloping it while wearing itself.

The wear amount of the friction body 3 is represented by the tensile strength at break Tb and elongation at break Eb calculated in accordance with, for example, "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties" specified in JIS K 6251:2017 of the Japanese Industrial Standards. The tensile strength at break Tb is the tensile force recorded when the measured object is broken divided by the cross-sectional area of the measured object before the test. The elongation at break Eb is the elongation when the measured object is broken, and is expressed as a ratio (%) of the length of the measured object before the test.

The inventor has found that the wear amount of the friction body 3 is inversely proportional to Tb x Eb. In other words, the wear amount of the friction body 3 is affected by the mechanical strength and elongation rate of the material. By combining the tensile strength at break Tb and the elongation at break Eb to appropriate values, the wear amount of the friction body 3 can be controlled. The value of Tb x Eb represents the energy required to wear the friction body 3. Therefore, the more easily the measured object wears, the smaller the value of Tb x Eb, and the more difficult the measured object wears, the larger the value of Tb x Eb.

It is preferable that the value of Tb × Eb of the material of the friction body 3 calculated by a method conforming to JIS K 6251:2017 satisfies the following condition iii).
iii) 5000≦Tb×Eb≦18000
In the above iii) the unit of the tensile strength at break Tb is "MPa" and the unit of the elongation at break Eb is "%", but these may be converted into other units.

In the above iii), 8000≦Tb×Eb≦16000 is preferable, and 10000≦Tb×Eb≦14000 is more preferable. When the material of the friction body 3 satisfies the above iii), the friction body 3 generates an appropriate amount of wear debris by normal frictional action by hand. This makes it possible for the metallic luster pigment added to the thermochromic ink to adhere to and encase the wear debris.

In the above iii), if the value of Tb×Eb exceeds 18,000, it becomes difficult to wear down the friction body 3 by normal manual friction. For this reason, it is not possible to attach the metallic luster pigment to the wear debris and envelop it while wearing down the friction body 3.

On the other hand, in the above iii), if the value of Tb×Eb is smaller than 5000, the friction body 3 is easily worn down by normal manual friction. As a result, the frictional heat generated by the friction body 3 is lost together with the wear debris, making it difficult to efficiently thermo-change the color of the thermochromic ink.

4. Core The core 7 is made of a synthetic resin or metal harder than the friction body 3. The material constituting the core 7 will be described later. The core 7 in this embodiment is a small cylindrical part having an outer diameter substantially the same as the inner diameter of the inner hole 31. Such a core 7 is inserted into the inner hole 31 of the friction body 3. The outer peripheral surface of the core 7 comes into contact with the inner peripheral surface of the inner hole 31, so that the friction body 3 is firmly fixed to the mounting hole 2 of the barrel 1. This increases the rigidity of the entire friction portion 32, and prevents the friction portion 32 from deforming. As a result, even if the hardness of the material of the friction body 3 is reduced, good friction performance can be exhibited.

In addition, the outer peripheral surface of the core 7 comes into contact with the inner peripheral surface of the inner hole 31, increasing the rigidity of the outward protrusions 51 provided on the mounting portion 5 of the friction body 3, suppressing inward deformation of the outward protrusions 51. This firmly engages the outward protrusions 51 with the inward protrusions 21, preventing the friction body 3 from falling off the mounting hole 2.

Furthermore, it is preferable that the outer peripheral surface of the core 7 is pressed against the inner peripheral surface of the inner hole 31, rather than simply contacting it. In order to press the outer peripheral surface of the core 7 against the inner peripheral surface of the inner hole 31, the outer diameter of the core 7 should be set to be equal to or larger than the inner diameter of the inner hole 31. Pressing the outer peripheral surface of the core 7 against the inner peripheral surface of the inner hole 31 increases the rigidity of the friction portion 32 and the outward protrusions 51, and more reliably prevents the core 7 and friction body 3 from falling off.

Here, the "rigidity" of the friction portion 32 refers to the deformation resistance of the friction portion 32 against an external force, and includes tensile rigidity, compressive rigidity, bending rigidity, shear rigidity, torsional rigidity, etc. The external force is mainly a force applied to the friction portion 32 during frictional operation. It is preferable that the friction portion 32 has a rigidity that does not buckle due to the external force during frictional operation.

4.1 Material of the Core The core 7 is made of a synthetic resin or metal harder than the friction body 3. As the synthetic resin, for example, polypropylene, polyethylene, polystyrene, polycarbonate, polyethylene terephthalate, polyacetal, acrylic, nylon, acrylonitrile-styrene copolymer resin (AS resin), acrylonitrile-butadiene-styrene copolymer resin (ABS resin), etc. can be used. In addition, a rubber or elastomer harder than the friction body 3 may be used. As the rubber or elastomer, for example, silicone resin, SBS resin (styrene-butadiene-styrene copolymer), SEBS resin (styrene-ethylene-butylene-styrene copolymer), fluorine-based resin, chloroprene resin, nitrile resin, polyester-based resin, ethylene propylene diene rubber (EPDM) can be used. The synthetic resin core 7 can be manufactured by cutting or injection molding. Furthermore, as the metal, for example, aluminum alloy, stainless steel, brass, etc. can be used. On the other hand, the metal core 7 can be manufactured by, for example, cutting or plastic processing.

4.2 Shape of the core As shown in Fig. 4, the core 7 is preferably symmetrical with respect to the horizontal central axis. By making the core 7 symmetrical, there is no distinction between the top and bottom of the core 7, and the core 7 can be inserted into the inner hole 31 from either the top or bottom. Conversely, the core 7 may be asymmetrical. For example, at least the edge portion of the upper end of the core 7 may be chamfered to facilitate insertion into the inner hole 31.

4.3 Ventilation Part The inner hole 31 in this embodiment is a hole that opens at the lower end of the attachment part 5 and does not open at the upper end of the friction part 32, and is closed on one side. On the other hand, the core 7 is a small cylindrical part having an outer diameter equal to or larger than the inner diameter of the inner hole 31. When such a core 7 is inserted into the inner hole 31 with one side closed, the air in the inner hole 31 is compressed by the core 7, and the core 7 may not be smoothly inserted into the inner hole 31. Therefore, the core 7 is provided with a ventilation part 71. The ventilation part 71 in this embodiment is a through hole that penetrates from one end to the other end of the core 7 along the central axis in the vertical direction of the core 7. In the process of inserting the core 7 into the inner hole 31, the air in the inner hole 31 passes through the ventilation part 71 and is discharged to the outside. Such ventilation part 71 makes it easier to insert the core 7 into the inner hole 31, and allows the core 7 to be inserted by an automatic assembly machine.

Note that the ventilation part 71 is not limited to the configuration shown in FIG. 4. For example, the cross-sectional shape of the ventilation part 71 is not limited to a circle, and may be a shape other than a circle. The ventilation part 71 may be provided shifted from the central axis of the core 7. Furthermore, the ventilation part 71 is not limited to a through hole, and may be, for example, at least one groove or protrusion provided on the outer peripheral surface of the core 7. For example, the ventilation part 71 may be a spiral groove or protrusion provided along the outer peripheral surface of the core 7. The spiral groove or protrusion has an anti-slip effect that prevents the core 7 from falling off the inner hole 31. Furthermore, instead of providing the ventilation part 71 on the core 7, the above-mentioned groove or protrusion may be provided on the inner peripheral surface of the inner hole 31.

4.4 Upper core portion and lower core portion In this embodiment, the upper half of the core 7 is called the upper core portion 72, and the lower half of the core 7 is called the lower core portion 73. As already mentioned, the core 7 is cylindrical with the same outer diameter over its entire length. However, the core 7 may be tapered so that the outer diameter of the lower core portion 73 is larger than the outer diameter of the upper core portion 72. This makes it easier to insert the core 7 into the inner hole 31. In addition, the larger outer diameter of the lower core portion 73 increases the rigidity of the outward protrusions 51, and prevents the outward protrusions 51 from deforming inward. This firmly engages the outward protrusions 51 and the inward protrusions 21, preventing the friction body 3 from falling off.

4.5 Retention of the core In order to prevent the core 7 inserted into the inner hole 31 from easily slipping out, a non-slip surface can be provided on the outer circumferential surface of the core 7. To prevent slipping, for example, the outer circumferential surface of the core 7 may be roughened to increase the frictional resistance against the inner circumferential surface of the inner hole 31. Also, minute protrusions may be provided on the outer circumferential surface of the core 7 to prevent slipping. Furthermore, the outer diameter of the core 7 may be made significantly larger than the inner diameter of the inner hole 31 to prevent the core 7 from easily slipping out of the inner hole 31.

5. Method of Mounting Friction Body Next, a method of mounting the friction body 3 according to this embodiment will be described with reference to FIGS.

As shown in Figure 1, the friction body 3 is placed above the mounting hole 2 at the rear end of the barrel 1, and then dropped directly into the mounting hole 2. Then, as shown in Figure 2, the cylindrical portion 53 of the mounting part 5 enters the minimum inner diameter portion 21b of the mounting hole 2, and the mounting part 5 is temporarily inserted into the mounting hole 2. At this time, the guide surface 51a of the mounting part 5 abuts against the guide surface 21a of the mounting hole 2, so that the temporarily inserted state of the mounting part 5 is stably maintained.

Next, the friction body 3 in the provisionally inserted state is pushed into the mounting hole 2. Then, the outward protrusion 51 of the mounting portion 5 overcomes the inward protrusion 21 of the mounting hole 2. At this time, the outward protrusion 51 is strongly pressed against the inward protrusion 21, so that the middle portion of the mounting portion 5 elastically deforms and bulges radially outward. The middle portion of the mounting portion 5 bulging radially outward is accommodated in the annular space 6 in the mounting hole 2. As a result, the middle portion of the mounting portion 5 is not pressed against the inner circumferential surface near the entrance of the mounting hole 2, and does not interfere with the insertion of the mounting portion 5. Therefore, the outward protrusion 51 smoothly passes over the inward protrusion 21, and the outward protrusion 51 and the inward protrusion 21 are engaged. This completes the insertion of the mounting portion 5 into the mounting hole 2 (see FIG. 3).

Then, as shown in Figure 4, the core 7 is inserted into the inner hole 31 of the friction body 3. In the process of inserting the core 7 into the inner hole 31, the air inside the inner hole 31 passes through the ventilation section 71 and is discharged to the outside. Such ventilation section 71 makes it easy to insert the core 7 into the inner hole 31. The core 7 inserted into the inner hole 31 presses the mounting section 5 outward, strengthening the engagement between the outward projection 51 and the inward projection 21. This completes the attachment of the friction body 3 to the rear end of the barrel 1.

According to the method for mounting the friction body 3 of this embodiment, the flexible mounting portion 5 can be inserted into the mounting hole 2 at a stage before inserting the core 7 into the inner hole 31, and the outward protrusions 51 and the inward protrusions 21 can be easily engaged. Then, by inserting the core 7 into the inner hole 31, a force acts in the inward and outward directions on the mounting portion 5, and the engagement between the outward protrusions 51 and the inward protrusions 21 is firmly maintained. In addition, since the core 7 is inserted into the inner hole 31 after the mounting portion 5 is inserted into the mounting hole 2, the mounting work of the friction body 3 shown in Figures 1 to 4 does not require a large force.

6. Thermochromic ink The thermochromic ink contained in the thermochromic writing instrument of this embodiment may be any of water-based ink, oil-based ink, and gel ink, as long as it can form a thermochromic mark. The form of the thermochromic ink is not limited to liquid, and may be solid, such as a pencil lead. The thermochromic ink will be described in detail below.

The thermochromic ink incorporated in the thermochromic writing implement is one that changes color or fades when heated. As the colorant added to the thermochromic ink, it is preferable to use a reversible thermochromic composition that contains an electron-donating color-forming organic compound, an electron-accepting compound, and a reaction medium for determining the temperature at which the color reaction of these compounds occurs. In particular, a microencapsulated pigment in which the reversible thermochromic composition is encapsulated in a microcapsule is more preferable.

The first reversible thermochromic composition is described, for example, in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, and Japanese Patent Publication No. 1-29398. The reversible thermochromic compositions described in these publications have a color change point on both the high-temperature side and the low-temperature side. The color change point refers to a predetermined temperature that is the boundary at which color change occurs. The first reversible thermochromic composition becomes a decolorized state in a temperature range above the high-temperature side color change point, and becomes a colored state in a temperature range below the low-temperature side color change point. In the normal temperature range, either the decolorized state or the colored state is maintained. The other state is maintained only while the temperature of the high-temperature side color change point or the low-temperature side color change point is reached. When the temperature of the high-temperature side color change point or the low-temperature side color change point is no longer reached, the first reversible thermochromic composition returns to one of the states. In other words, the first reversible thermochromic composition has a relatively small hysteresis characteristic width ΔH (for example, ΔH is 1°C or more and 7°C or less).

As a second reversible thermochromic composition, for example, JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, JP-A-2006-137886, JP-A-2006-188660, JP-A-2008-45062, and JP-A-2008-280523 describe reversible thermochromic compositions having a large hysteresis characteristic width ΔH (for example, a ΔH value of 8°C or more and 50°C or less).

Here, the magnitude of the width ΔH of the hysteresis characteristic is indicated by the shape of the curve plotting the color density of the reversible thermochromic composition versus temperature. For example, assume that the reversible thermochromic composition is in a completely decolorized state in a temperature range above the high-temperature discoloration point, and in a completely colored state in a temperature range below the low-temperature discoloration point. The temperature at which the composition is in a completely decolorized state is called the "complete decolorization temperature," and the temperature at which the composition is in a completely colored state is called the "complete color development temperature." In the curve plotting the color density of this reversible thermochromic composition versus temperature, if the path of the curve from the low-temperature completely decolorization temperature to the high-temperature completely color development temperature is significantly different from the path of the curve from the high-temperature completely color development temperature to the low-temperature completely decolorization temperature, the width ΔH of the hysteresis characteristic is large. Furthermore, such a reversible thermochromic composition has a color memory property that maintains a colored or decolored state in a specific temperature range, for example, in the normal temperature range (daily living temperature range).

In a reversible thermochromic composition having color memory, it is preferable that the complete coloring temperature is set to a low temperature outside the room temperature range, and the complete decolorization temperature is set to the temperature of frictional heat that can be generated by a friction body. The complete coloring temperature is, for example, in the range of -50°C to 0°C, preferably -40°C to -5°C, more preferably -30°C to -10°C. On the other hand, the complete decolorization temperature is, for example, in the range of 50°C to 95°C, preferably 50°C to 90°C, more preferably 60°C to 80°C. Furthermore, by setting the width ΔH of the hysteresis characteristic to 40°C to 100°C, the colored state or decolorized state is well maintained in the room temperature range.

By encapsulating the above-mentioned reversible thermochromic composition in a microcapsule, a thermally decolorizable microcapsule pigment can be manufactured. The average particle size of the microcapsule pigment is, for example, in the range of 0.05 μm to 5.0 μm, preferably 0.1 μm to 4.0 μm, and more preferably 0.5 μm to 3.0 μm. This improves the writing performance and writing density of the thermochromic writing instrument. Furthermore, when the average particle size of the microcapsule pigment is 2.0 μm or more, it is possible not only to chemically decolorize the handwriting of the thermochromic ink, but also to physically erase it from the paper surface. In other words, a microcapsule pigment with an average particle size of 2.0 μm or more is physically peeled off from the paper surface by being adsorbed to a friction body, and is irreversibly erased.

The average particle diameter of the microencapsulated pigment is measured using image analysis particle size distribution measurement software "Mac-View" manufactured by MOUNTECH Co., Ltd. First, the particle region of the microencapsulated pigment is identified, then the projected area equivalent circle diameter (Heywood diameter) is calculated from the area of the particle region, and then the average particle diameter of particles equivalent to a sphere of equal volume is measured based on the projected area equivalent circle diameter value.

In addition, when the particle diameter of all or most of the microencapsulated pigments contained in the thermochromic ink exceeds 0.2 μm, it is possible to measure it using a particle size distribution measuring device "Multisizer (registered trademark) 4e" manufactured by Beckman Coulter, Inc. In this case, the equivalent volume sphere diameter of the microencapsulated pigment is measured by the Coulter method, and the average particle diameter is calculated based on this measurement value.

Furthermore, general dyes and pigments that do not have thermochromic properties may be added as coloring components. This makes it possible to impart the desired color that does not change color with heat to the handwriting of the thermochromic ink. For example, acid dyes, basic dyes, direct dyes, etc. can be used as general dyes. For example, inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, and dispersed pigment products that have been finely and stably dispersed in a medium using a surfactant can be used as general pigments. In addition, metallic luster pigments such as metal powder and pearl pigments, fluorescent pigments, phosphorescent pigments, and special pigments such as titanium dioxide can also be used. These coloring components may be used in combination with the above-mentioned microcapsule pigments, or may be encapsulated in the microcapsule pigments.

6.1 Metallic Pigment By adding a metallic pigment to a thermochromic ink, the thermochromic ink becomes metallic and a glittering handwriting is formed. Preferably, a transparent metallic pigment is added to the thermochromic ink. The transparent metallic pigment imparts glitter to the handwriting of the thermochromic ink, and when the handwriting of the thermochromic ink is chemically erased, it appears as if it has been completely erased without any glittering.

Transparent metallic luster pigments may be used that have a core material coated with a metal oxide, or a cholesteric liquid crystal type luster pigment. For example, materials selected from natural mica, synthetic mica, flat glass flakes, and flaky aluminum oxide may be used as the core material.

Effective luster pigments with natural mica as the core material are those with the surface coated with titanium oxide, or those with the upper layer of the titanium oxide coated with iron oxide or a non-thermochromic dye pigment. Examples of luster pigments with natural mica as the core material include those manufactured by Merck KGaA under the trade name "Iriodin (registered trademark)" and those manufactured by BASF SE under the trade name "Lumina (registered trademark)".

For the luster pigments with synthetic mica as the core material, it is effective to use those whose surface is coated with a metal oxide such as titanium oxide. For example, oxides of titanium, zirconium, chromium, vanadium, iron, etc. can be used as the metal oxide, and metal oxides whose main component is titanium oxide are preferred. For example, the product name "ULTIMICA (registered trademark)" manufactured by Nihon Koken Kogyo Co., Ltd. can be used as a luster pigment in which the surface of synthetic mica is coated with a metal oxide.

For the glittering pigments that have flat glass pieces as the core material, it is effective to use those whose surfaces are coated with a metal oxide such as titanium oxide. For example, the product name "Metashine (registered trademark)" manufactured by Nippon Sheet Glass Co., Ltd. can be used as a glittering pigment in which the surface of flat glass pieces is coated with a metal oxide.

For the glitter pigments with flaky aluminum oxide as the core material, it is effective to use those whose surface is coated with a metal oxide such as titanium oxide. For example, oxides of titanium, zirconium, chromium, vanadium, iron, etc. can be used as the metal oxide, and metal oxides whose main component is titanium oxide are preferred. For example, the product name "Xirallic (registered trademark)" manufactured by Merck KGaA can be used as a glitter pigment in which the surface of flaky aluminum oxide is coated with a metal oxide.

The liquid crystal polymer used as the cholesteric liquid crystal type luster pigment has the property of reflecting light in a certain region of the light incident in a wide spectral region and transmitting all light in other regions due to the optical interference effect. Cholesteric liquid crystal type luster pigment has excellent metallic luster, color flop properties in which the hue changes depending on the viewpoint, and transparency. For example, the product name "HELICONE (registered trademark) HC" manufactured by Wacker Chemie AG can be used as the cholesteric liquid crystal type luster pigment.

It is also possible to use photoluminescent materials manufactured by vacuum deposition. These photoluminescent materials are manufactured by vacuum depositing metals such as gold and silver onto a film to form a foil, which is then peeled off from the film and finely pulverized. As such a photoluminescent material, the product name "LG neo (registered trademark)" manufactured by Oike Kogyo Co., Ltd. can be used.

The average particle size of the metallic luster pigment described above is in the range of 0.1 μm to 50 μm, preferably 2 μm to 40 μm, and more preferably 10 μm to 40 μm. This improves the writing performance and handwriting brightness of the thermochromic writing instrument. As a method for measuring the average particle size of the metallic luster pigment, for example, the particle size distribution is measured using a particle size distribution measuring device "LA-300" manufactured by Horiba, Ltd., and the average particle size (median size) is calculated on a volume basis based on the measured value of this particle size distribution.

6.2 Physical erasure of metallic pigments Metallic pigments do not easily penetrate the paper surface. Therefore, when handwriting of thermochromic ink containing metallic pigments is rubbed, the metallic pigments scatter on the paper surface, and the appearance after erasing the handwriting becomes poor. In particular, on black paper, the shine of the metallic pigments is emphasized, and the appearance after erasing the handwriting becomes even worse.

Therefore, the material of the friction body 3 of this embodiment satisfies the above condition i) that the Shore A hardness value immediately after the indentation of the indentation needle is 60 or more and 85 or less. This allows the friction body 3 to enter into the depression of the handwriting formed on the paper surface. In addition, the material of the friction body 3 of this embodiment satisfies the above condition ii) that the ΔHS value is 0 or more and less than 5. This allows the friction body 3 to adsorb and peel off the metallic luster pigment from within the depression of the handwriting. In other words, according to the friction body 3 of this embodiment, it is possible to physically erase the metallic luster pigment added to the thermochromic ink without scattering it on the paper surface. In addition, the handwriting of the thermochromic ink is chemically erased by frictional heat.

Furthermore, when a metallic luster pigment is added to the thermochromic ink, it is preferable that the volume Vp of the metallic luster pigment and the volume Ve of the friction portion 32 satisfy the following condition iv).
iv) 5≦Ve/Vp≦35

The volume Vp of the metallic luster pigment indicates the amount of metallic luster pigment that gives the handwriting a brilliance. The volume Ve of the friction portion 32 indicates the amount of the friction portion 32 that physically erases the metallic luster pigment by wearing it. By setting the value of Ve/Vp within the range of 5 to 35, a balance is maintained between the amount of metallic luster pigment added to the thermochromic ink and the amount of the friction portion 32 required to erase this amount of metallic luster pigment. In other words, when Ve/Vp is the upper limit of 35, the metallic luster pigment is the minimum amount that gives the handwriting a visible brilliance. In this case, the friction portion 32 is the maximum amount that can erase the minimum amount of metallic luster pigment 100%. On the other hand, when Ve/Vp is the lower limit of 5, the metallic luster pigment is the maximum amount that gives the handwriting a high brilliance. In this case, the friction portion 32 is the minimum amount that can erase the maximum amount of metallic luster pigment 30%. The value of Ve/Vp is preferably 8 to 26, more preferably 10 to 20.

6.3 Other Additives Various additives known in the art may be added to the thermochromic ink. When the thermochromic ink is water-based, for example, pH adjusters, rust inhibitors, preservatives, antifungal agents, wetting agents, defoamers, surfactants, lubricants, fixing agents such as resins, shear thinning agents, pen tip drying inhibitors, sagging inhibitors, etc. may be added. When the thermochromic ink is oil-based, for example, viscosity adjusters, preservatives, rust inhibitors, defoamers, lubricants, dispersants, anti-scratch agents, anti-leak agents, surfactants, etc. may be added.

7. Thermochromic Writing Instrument The type of the thermochromic writing instrument of this embodiment is not particularly limited, and may be, for example, any of a fountain pen, a marking pen, a ballpoint pen, a retractable solid writing instrument, and the like. The thermochromic writing instrument may be either a cap type or a retractable type. The cap type thermochromic writing instrument is provided with a cap for covering the nib (tip). The retractable thermochromic writing instrument is provided with a retractable mechanism capable of putting the nib in a protruding state from the barrel and in a retracted state in which the nib is stored in the barrel. The retractable mechanism may be, for example, a knock type, a rotating type, a sliding type, or the like. Furthermore, the retractable thermochromic writing instrument may be provided with two or more refills, and may be configured to selectively put any one of the two or more refills in a protruding state. In this case, the two or more refills may be configured to have different types of nibs and/or thermochromic inks of different colors.

The tip of the marking pen may be, for example, a fiber tip, a felt tip, a plastic tip, a metal tip, or the like. The thermochromic ink used in the marking pen may be impregnated in an ink absorbing body made of a fiber bundle. The ink absorbing body is housed in a barrel. The thermochromic ink impregnated in the ink absorbing body is supplied to the pen tip. The thermochromic ink used in the marking pen may also be directly housed in the barrel. In this case, the barrel is provided with an ink flow rate adjustment member made of a comb groove or a fiber bundle. The thermochromic ink directly housed in the barrel is supplied to the pen tip via the ink flow rate adjustment member. The barrel may be provided with a valve mechanism that supplies a predetermined amount of ink to the pen tip instead of the ink flow rate adjustment member.

The thermochromic ink used in the ballpoint pen is filled, for example, in an ink reservoir tube with a ballpoint tip attached to the tip. In this case, an ink backflow prevention body is placed at the rear end of the thermochromic ink in the ink reservoir tube. The thermochromic ink used in the ballpoint pen may also be directly contained in the barrel. In this case, an ink backflow prevention body is placed at the rear end of the thermochromic ink in the barrel. Furthermore, the thermochromic ink used in the ballpoint pen may be impregnated in an ink occlusion body made of fiber bundles. The barrel may be provided with an ink flow rate adjustment member made of a comb groove or fiber bundle. A predetermined amount of thermochromic ink is supplied to the pen tip via the ink flow rate adjustment member.

In the various types of thermochromic writing instruments described above, the friction body 3 of this embodiment is attached to any of the components constituting the thermochromic writing instrument, thereby becoming one with the thermochromic writing instrument (see FIG. 5). For example, the friction body 3 is attached to the cap, clip, head cap, ferrule, barrel, tail cap, grip, and operating part for extending and retracting the pen tip that constitute the thermochromic writing instrument. The friction part 32 may be covered with a cover to prevent dirt.

In addition, the friction body 3 of this embodiment may not be attached to any of the components constituting the thermochromic writing instrument, and may be separate from the thermochromic writing instrument (see FIG. 6). The separate friction body 3 may be configured to be made only of the above-mentioned low-hardness synthetic resin material. The separate friction body 3 may also be configured to be attached to another component made of a high-hardness material.

8. Effects The friction body 3 of this embodiment, like conventional friction bodies, can discolor or erase handwriting of thermochromic ink by generating frictional heat. Furthermore, the frictional portion 32, which has low hardness, penetrates into the depressions of the handwriting, adsorbs the metallic luster pigment added to the thermochromic ink, and peels it off from the paper surface. The metallic luster pigment adsorbed to the frictional portion 32 is caught up in the wear debris of the frictional portion 32 and is completely removed from the paper surface. In this way, the frictional body 3 of this embodiment can chemically and physically erase handwriting of thermochromic ink to which a metallic luster pigment has been added.

By using the friction body 3 of this embodiment, handwriting of thermochromic ink containing metallic luster pigment can be erased without leaving any color. Therefore, the appearance of the paper surface after erasing the handwriting is good. In particular, metallic luster pigments with an average particle size of 10 μm or more can give high brilliance to handwriting of thermochromic ink and are easily adsorbed to the friction part 32.

Here, the conventional friction body cannot erase the handwriting of the pencil lead because the Shore A hardness value is too large. In order to erase the handwriting of the pencil lead, it is necessary to use an eraser with a small Shore A hardness value. In contrast, the friction body 3 of this embodiment has a Shore A hardness value smaller than that of the conventional friction body. In addition, the friction body 3 has a property similar to that of an eraser, in that it is scraped off by rubbing the paper surface and generates a small amount of wear debris. Therefore, it is possible to erase both the handwriting of the thermochromic ink and the handwriting of the pencil lead with one friction body 3.

Note that the friction body 3 in this embodiment may be separate from the thermochromic writing instrument (see friction body 201 in FIG. 6). The friction body 3 separate from the thermochromic writing instrument is preferably attached to a support for holding with the fingers. The support is formed, for example, from a hard synthetic resin or metal. The friction body 3 separate from the thermochromic writing instrument is combined with the thermochromic writing instrument to form one writing set.

Below, examples of the thermochromic writing implement of the present invention will be described with reference to Figures 5 and 6. In the first and second examples described below, the numerical values indicating the content of the composition indicate parts by mass. The average particle size of the thermochromic pigment was measured using a particle size distribution measuring device "Multisizer (registered trademark) 4e" manufactured by Beckman Coulter, Inc. The equivalent volume sphere diameter of the thermochromic pigment was measured by the Coulter method, and the average particle size was calculated from this measurement. The average particle size of the metallic luster pigment was measured using a particle size distribution measuring device "LA-300" manufactured by Horiba, Ltd. The particle size distribution of the metallic luster pigment was measured, and the average particle size (median diameter) was calculated on a volume basis based on this measurement. The Shore A hardness of the material of the friction body was measured by a test method conforming to JIS K 7215 of the Japanese Industrial Standards. A sample of a predetermined shape, thickness and size was prepared using the same material as the friction body. The sample was pressed with a manual durometer to measure the Shore A hardness.

First Example In the first example, the thermochromic writing instrument 103 of the second embodiment shown in Fig. 5 was used. The thermochromic writing instrument 103 has a shaft tube 182 with a friction body 101 attached to the rear end thereof.

The friction body 101 is formed of a polyester-based elastomer that satisfies the above conditions i) to iv). The Shore A hardness value of the polyester-based elastomer immediately after the initiation of the indenter contact was 70, and the Shore A hardness value 15 seconds after the initiation of the indenter contact was 69. Therefore, the ΔHS value of the polyester-based elastomer is 1.

The tensile strength at break Tb and elongation at break Eb of the polyester-based elastomer were measured using a test method conforming to JIS K 6251:2017. As a result of the measurement, the tensile strength at break Tb was 14 MPa, and the elongation at break Eb was 890%. Therefore, the value of Tb x Eb of the polyester-based elastomer is 12,460.

The above-mentioned polyester elastomer was injection molded to obtain a milky white friction body 101 having the shape shown in Figure 5. The friction body 101 has a friction portion 111 having a convex curved surface shape and a cylindrical mounting portion 112. A stepped locking portion is formed at the lower end of the mounting portion 112. By making the friction portion 111 have a convex curved surface shape, the friction action is stabilized, making it easier to rub handwriting on paper.

The mounting portion 112 of the friction body 101 is inserted into a mounting hole 181 provided at the rear end of the shaft tube 182. Two ring beads are formed on the inner circumferential surface of the mounting hole 181. The mounting portion 112 is sandwiched between the two ring beads within the mounting hole 181. Furthermore, the locking portion of the mounting portion 112 is locked to the lower end of the mounting hole 181. The maximum outer diameter D of the friction portion 111 is 6, and the projection length L from the mounting hole 181 is also 6. Therefore, the L/D value of the friction portion 111 is 1.

The thermochromic writing instrument 103 is a retractable ballpoint pen. The pen tip (ballpoint pen tip) 105 of the thermochromic writing instrument 103 is brought into a protruding or retracted state by sliding the operating part 184 forward. The operating part 184 protrudes to the outside from the side of the barrel 182. A retraction mechanism for retracting the pen tip 105 is housed inside the barrel 182. The retraction mechanism is mainly composed of a sliding body 184a , a refill holding part 185, a coil spring 183, and a locking member 186. The refill 104 is housed in front of the refill holding part 185 inside the barrel 182.

The barrel 182 is composed of a front barrel 182b and a rear barrel 182a. An opening 182c is provided at the tip of the front barrel 182b. The opening 182c has a diameter that allows the pen tip 105 of the refill 104 to protrude or retract. The rear barrel 182a is screwed to the rear end of the front barrel 182b. The above-mentioned retraction mechanism is housed inside the rear barrel 182b. In order to house the sliding body 184a integrally molded with the operating unit 184, the rear barrel 182a is composed of first and second parts that can be separated in the front-rear direction. A slide hole extending in the front-rear direction is formed in the second part that constitutes the rear of the rear barrel 182a. When the sliding body 184a is housed inside the rear barrel 182a, the operating unit 184 protrudes to the outside from the slide hole.

The sliding body 184a is a substantially cylindrical resin molding integrally molded with the operating unit 184. A plurality of sawtooth-shaped protrusions are formed at the tip of the sliding body 184a. The refill holding part 185 is disposed in front of the sliding body 184a in the rear shaft 182a. The refill holding part 185 is a substantially cylindrical resin molding that fits into the rear end of the refill 104. A plurality of steps are formed at the rear end of the refill holding part 185. The plurality of steps mesh with the sawtooth-shaped protrusions of the sliding body 184a. In addition, a plurality of ribs extending in the axial direction are formed at equal intervals on the outer peripheral surface of the refill holding part 185. On the other hand, a plurality of grooves are formed at equal intervals on the inner surface of the first part that constitutes the front of the rear shaft 182a. The plurality of grooves guide the plurality of ribs of the refill holding part 185 in the axial direction.

The front end of the refill holding portion 185 has a smaller outer diameter than the other portions and is inserted into the rear end of the coil spring 183. The front end of the coil spring 183 is engaged with a locking member 186 fixed inside the rear shaft 182a. The coil spring 183 biases the refill holding portion 185 and the refill 104 rearward.

When the operating unit 184 is slid forward with the pen tip 105 retracted, the multiple ribs of the refill holding unit 185 are guided into the multiple grooves in the rear shaft 182a, and the refill holding unit 185 moves forward. When the multiple ribs pass through the multiple grooves, the sawtooth convex portion of the sliding body 184a engages with the stepped portion of the refill holding unit 185, rotating the refill holding unit 185 by a predetermined angle. This causes the end faces of the multiple ribs to abut against the end faces of the multiple grooves, and the refill holding unit 185 is fixed in the forward moving state. As a result, the pen tip 105 of the refill 104 is maintained in a state protruding from the opening 182c of the front shaft 182b.

When the operating part 184 is slid forward with the pen tip 105 protruding, the sawtooth convex part of the sliding body 184a engages with the step part of the refill holding part 185, rotating the refill holding part 185 by a predetermined angle. This releases the contact between the end faces of the multiple ribs and the end faces of the multiple grooves, and the multiple ribs of the refill holding part 185 are guided into the multiple grooves in the rear shaft 182a. The refill holding part 185 moves rearward due to the biasing force of the coil spring 183. As a result, the pen tip 105 of the refill 104 is immersed in the opening 182c of the front shaft 182b.

The refill 104 is composed of a pen tip 105, an ink reservoir tube 106, and a connecting member 107. A ball is rotatably held at the front end of the pen tip 105. The ink reservoir tube 106 is a metal pipe with openings at the front and rear ends. The connecting member 107 is formed from a transparent synthetic resin. The pen tip 105 is connected to the opening at the front end of the ink reservoir tube 106 via the connecting member 107. A thermochromic ink composition 161 and an ink follower composition 162 are contained in the refill 104.

The components of thermochromic ink composition 161 are reversible thermochromic pigment (11 parts), transparent metallic luster pigment (3 parts), metal vapor deposition resin pigment (2 parts), shear thinning agent (0.3 parts), urea (10 parts), glycerin (10 parts), nonionic penetrating agent (0.6 parts), hydrophobic silica-based defoamer (0.1 part), preservative (0.1 part) and water (62.9 parts).

The reversible thermochromic pigment is a microcapsule containing a reversible thermochromic composition that changes color from pink to colorless. The reversible thermochromic pigment has a color-developing temperature of -10°C, a color-fading temperature of 65°C, and an average particle size of 2.5 μm.

As the transparent metallic luster pigment, the product name "Iriodin (registered trademark) 6103 Icy White" manufactured by Merck KGaA was used. This transparent metallic luster pigment is composed of silver particles in which the surface of synthetic mica is coated with metal oxide. The average particle diameter of the transparent metallic luster pigment is 25 μm. As the metal vapor deposition resin pigment, the product name "LGneo (registered trademark) Silver #325" manufactured by Oike Kogyo Co., Ltd. was used. The color of the particles of this metal vapor deposition resin pigment is silver, and the average particle diameter is 35 μm. The ratio Ve/Vp of the volume Ve of the friction part 111 to the total volume Vp of the transparent metallic luster pigment and the metal vapor deposition resin pigment is 15.

Xanthan gum was used as the shear thinning agent. SN Wet 366, a product name manufactured by San Nopco Ltd., was used as the nonionic penetrating agent. Nopco 8034, a product name manufactured by San Nopco Ltd., was used as the hydrophobic silica-based defoaming agent. Proxel (registered trademark) XL2, a product name manufactured by Lonza Japan Ltd., was used as the preservative.

The components of the ink follower composition 162 are polybutene (98.5 parts) as a base oil and fatty acid amide (1.5 parts) as a thickener. The mixture of polybutene and fatty acid amide was kneaded with a three-roll mill to obtain the ink follower composition 162.

Using the thermochromic writing implement 103, a handwriting of the thermochromic ink composition 161 was formed on the surface of "writing paper A" (100% chemical pulp, whiteness 75.0 or more) conforming to the Japanese Industrial Standard JIS P3201. A pink thermochromic pigment was used as the base of the handwriting, and a silver transparent metallic luster pigment and a metal vapor deposition resin pigment were dispersed in the handwriting. As a result, the handwriting of the thermochromic ink composition 161 exhibited a metallic pink color on the white paper surface. In addition, a handwriting of the thermochromic ink composition 161 was formed on the black paper surface. As a result, the hue of the handwriting formed on the black paper surface was the same as that on the white paper surface. However, the brilliance of the handwriting formed on the black paper surface was particularly higher than that on the white paper surface.

The handwriting formed on the white and black paper surfaces can be chemically and physically erased by the friction body 101 attached to the thermochromic writing implement 103. That is, the handwriting formed on the paper surface is repeatedly rubbed by the friction part 111. Then, the friction part 111 generates frictional heat, and the thermochromic pigment in the handwriting changes color from pink to colorless and transparent. In addition, the friction part 111, which has low hardness, penetrates into the depression of the handwriting, adsorbs the silver transparent metallic luster pigment and the metal vapor deposition resin pigment, and peels off from the paper surface. Furthermore, the transparent metallic luster pigment and the metal vapor deposition resin pigment adsorbed by the friction part 111 are wrapped up in the wear debris of the friction part 111 and are completely removed from the paper surface. In this way, the friction body 101 cleanly erases the handwriting of the thermochromic ink composition 161 without soiling the paper surface. In particular, the metallic luster pigment and the metal vapor deposition resin pigment remaining on the black paper have a problem of shining depending on the viewing angle and being visually recognized. This problem is solved by using the friction body 101 .

Table 1 below shows the results of the evaluation test of each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4. The friction bodies of Examples 1 to 4 meet all of the conditions of the present invention related to Shore A hardness and Ve/Vp. The friction bodies of Comparative Examples 1 to 4 do not meet either of the conditions of the present invention related to Shore A hardness and Ve/Vp. Each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4 has the same shape as the friction body 101 shown in FIG. 5 and is attached to the rear end of the barrel 182 of the thermochromic writing instrument 103. The refill 104 of the thermochromic writing instrument 103 contains the thermochromic ink composition 161 and the ink follower composition 162, which are composed of the above-mentioned components. The pen tip 105 of the refill 104 is a ballpoint pen tip.

The friction bodies of Examples 1 to 4 are all made of polyester-based elastomer. The hardness of the friction bodies of Examples 1 to 4 was varied by mixing polyester-based elastomers with different hardness. The friction bodies of Examples 1 to 4 all satisfy the conditions of the present invention, that is, the Shore A hardness immediately after the indenter starts to contact is 60 or more and 85 or less, the ΔHS value is 0 or more and less than 5, and the Ve/Vp value is 5 or more and 35 or less.

The friction body of Comparative Example 1 is made of a polyester-based elastomer having the same hardness as that of Example 1. The friction body of Comparative Example 1 has a Ve/Vp value of 4. In this respect, the friction body of Comparative Example 1 does not satisfy the condition of the present invention that the Ve/Vp value be 5 or more and 35 or less.

The friction body of Comparative Example 2 is composed of 40% α-polyolefin copolymer, 40% styrene-based elastomer, and 20% crystalline polypropylene. The friction body of Comparative Example 2 has a Shore A hardness value of 90 immediately after the indenter starts to contact the friction body, and a ΔHS value of 18. In these respects, the friction body of Comparative Example 2 does not satisfy the conditions of the present invention, that is, a Shore A hardness value of 60 to 85 immediately after the indenter starts to contact the friction body, and a ΔHS value of 0 to less than 5.

The friction body of Comparative Example 3 is made of a styrene-based elastomer (product name "AR-885C" by Aron Chemical Industries, Ltd.). The friction body of Comparative Example 3 has a Shore A hardness of 88 immediately after the indenter starts to contact the friction body of Comparative Example 3. In this respect, the friction body of Comparative Example 3 does not satisfy the condition of the present invention that the Shore A hardness immediately after the indenter starts to contact the friction body of Comparative Example 3 is 60 or more and 85 or less.

The friction body of Comparative Example 4 was made from a commercially available eraser made of polyvinyl chloride resin (product number "ER-F6" by Pilot Corporation). The friction body of Comparative Example 4 has a Shore A hardness value of 50 immediately after the indenter starts to contact the material, and a ΔHS value of 25. In these respects, the friction body of Comparative Example 4 does not satisfy the conditions of the present invention, that is, a Shore A hardness value of 60 to 85 immediately after the indenter starts to contact the material, and a ΔHS value of 0 to less than 5.

Using each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4, writing marks made with a thermochromic writing instrument 103 were erased, and the erasability, wear debris, continuous erasability, and erasable amount were evaluated as described below.

<Evaluation of erasability>
Eight sheets of white paper and eight sheets of black paper were prepared. The white paper was "writing paper A" (100% chemical pulp, whiteness 75.0 or more) conforming to JIS P3201 of the Japanese Industrial Standards. The black paper was black paper made of 100% chemical pulp. The thickness of the white paper and the black paper was 0.09 mm, and the basis weight was 80 g/ ^m2 . Using the thermochromic writing instrument 103, handwriting of the thermochromic ink composition 161 was formed on each of the white paper and the black paper. The handwriting was a circular spiral pattern. Ten spiral patterns were handwritten in one line on one sheet of paper. Then, the ten spiral patterns formed on each of the white paper and the black paper were erased using each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4. The state of the paper surface after erasure was visually confirmed.

The erasability evaluation in Table 1 is as follows.
A: The handwriting was erased without leaving any color.
B: The pink color of the thermochromic pigment or the silver color of the metallic luster pigment remained faintly.
C: The pink color of the thermochromic pigment or the silver color of the metallic luster pigment was not erased.

<Evaluation of wear debris>
In the evaluation of the erasability described above, ten spiral patterns formed on the surface of each of white and black paper were erased using each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4, and then the state of the wear debris generated from each of the friction bodies was visually confirmed.

The wear debris evaluation in Table 1 is as follows:
A: There was no problem in practical use.
B: Wear debris adhered to the friction body, causing problems in practical use.
C: A large amount of wear debris was generated, causing problems in practical use.

<Evaluation of continuous erasability>
Eight sheets of blank paper were prepared. The blank paper was "writing paper A" (100% chemical pulp, whiteness 75.0 or more) conforming to JIS P3201 of the Japanese Industrial Standards. The thickness of the blank paper was 0.09 mm, and the basis weight was 80 g/ ^m2 . Using the thermochromic writing implement 103, handwriting of the thermochromic ink composition 161 was formed on the surface of the blank paper. The handwriting was a circular spiral pattern. Ten spiral patterns were handwritten on each of 30 lines on one sheet of paper, for a total of 300 spiral patterns. Then, using each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4, the 30 lines of spiral patterns formed on each of the eight sheets of blank paper were continuously erased. In the process of erasing the 30 lines of spiral patterns, it was confirmed how many lines the friction performance of the friction body was maintained immediately after the start of erasing. In such an evaluation of continuous erasability, the erasability of the metallic luster pigment and the state of the wear debris were not taken into consideration.

The continuous erasability in Table 1 was evaluated as follows.
A: The friction performance immediately after the start of erasing was maintained until 30 lines of the spiral pattern were erased.
B: The friction performance immediately after the start of erasing was maintained until 20 lines of the spiral pattern were erased.
C: The friction performance immediately after the start of erasing was maintained until 10 lines of the spiral pattern were erased.

<Evaluation of erasable amount>
In the evaluation of the continuous erasability described above, the 30 lines of the spiral pattern were completely erased for each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4. Thereafter, the consumption amount of the thermochromic ink composition 161 for handwriting the 30 lines of the spiral pattern and the wear amount of the friction body for erasing the 30 lines of the spiral pattern were measured. Based on these measured values, the weight (erasable amount) of the thermochromic ink composition 161 that can be erased until the friction part of each of the friction bodies of Examples 1 to 4 and Comparative Examples 1 to 4 is completely worn away was calculated. The percentage of the weight of the ink contained in one refill 104 that this erasable amount corresponds to was clarified, and the practicality of the friction body was evaluated.

The erasable amount in Table 1 is evaluated as follows.
A: 30% or more of the ink weight of one refill can be erased, and there is no problem with practical use.
C: 30% or more of the ink weight of one refill cannot be erased, and there is a problem with its practicality.

Second Example In the second example, the friction body 201 of the third embodiment shown in Fig. 6 and a thermochromic writing instrument 203 were used. The configuration of the thermochromic writing instrument 203 is similar to that of the thermochromic writing instrument 103 of the first example described above. The friction body 201 is separate from the thermochromic writing instrument 203. The combination of the friction body 201 and the thermochromic writing instrument 203 constitutes one writing set 209.

The friction body 201 is fitted into the tip of the support 202 made of hard PP resin (polypropylene). The part of the friction body 201 protruding from the tip of the support 202 becomes the friction section 211. The friction section 211 is used to chemically and physically erase thermochromic ink to which a metallic luster pigment has been added. The cross sections of the friction body 201 and the support 202 are both elliptical. Seven friction bodies 201 were injection molded using the same materials as those of Examples 1 to 4 and Comparative Examples 1 to 3 in Table 1 above.

On the other hand, the components of the thermochromic ink composition 161 used in the thermochromic writing instrument 203 are the same as those in the first embodiment described above. That is, the components of the thermochromic ink composition 161 are reversible thermochromic pigment (11 parts), transparent metallic luster pigment (3 parts), metal vapor deposition resin pigment (2 parts), shear thinning agent (0.3 parts), urea (10 parts), glycerin (10 parts), nonionic penetrability agent (0.6 parts), hydrophobic silica-based defoamer (0.1 parts), preservative (0.1 parts), and water (62.9 parts).

However, the reversible thermochromic pigment was a microcapsule containing a reversible thermochromic composition that changes color from blue to colorless. The transparent metallic luster pigment was made by Merck KGaA under the trade name "Iriodin (registered trademark) 6107 Icy White Lightning". This transparent metallic pigment is made of silver particles with an average particle diameter of 25 μm.

As in the first embodiment described above, the thermochromic ink composition 161 is contained in the refill 104 of the thermochromic writing instrument 203. The pen tip of the refill 104 is a ballpoint pen tip. By sliding the operating portion 184 forward, the pen tip 105 of the refill 104 is brought into a protruding or retracted state.

Using the thermochromic writing implement 203, a handwriting of the thermochromic ink composition 161 was formed on the surface of "writing paper A" (100% chemical pulp, whiteness 75.0 or more) conforming to the Japanese Industrial Standard JIS P3201. A blue thermochromic pigment serves as the base of the handwriting, and a silver transparent metallic luster pigment and a metal vapor deposition resin pigment are dispersed in the handwriting. As a result, the handwriting of the thermochromic ink composition 161 appears metallic blue on the white paper surface. In addition, a handwriting of the thermochromic ink composition 161 was formed on the black paper surface. As a result, the hue of the handwriting formed on the black paper surface was the same as that on the white paper surface. However, the brilliance of the handwriting formed on the black paper surface was particularly higher than that on the white paper surface.

As described above, seven friction bodies 201 were injection molded using the same material as in Examples 1 to 4 and Comparative Examples 1 to 3 in Table 1. Seven writing sets 209 were constructed by combining each of the seven friction bodies 201 with a thermochromic writing implement 203. Each of the seven writing sets 209 was used to evaluate erasability, wear debris, continuous erasability, and erasable amount. The evaluation results were similar to those of Examples 1 to 4 and Comparative Examples 1 to 3 in Table 1.

All four friction bodies 201 made of the same material as Examples 1 to 4 in Table 1 showed good results in the erasability test. The handwriting of the thermochromic ink composition 161 is repeatedly rubbed by the friction part 211. Then, the friction part 211 generates frictional heat, and the thermochromic pigment in the handwriting changes color from blue to colorless and transparent. In addition, the friction part 211, which has low hardness, penetrates into the depressions of the handwriting, adsorbs the silver transparent metallic luster pigment and the metal-deposited resin pigment, and peels them off from the paper surface. Furthermore, the transparent metallic luster pigment and the metal-deposited resin pigment adsorbed by the friction part 211 are wrapped up in the wear debris of the friction part 211 and are completely removed from the paper surface. In this way, the friction body 201 cleanly erases the handwriting of the thermochromic ink composition 161 without soiling the paper surface. In particular, the transparent metallic luster pigment and the metal-deposited resin pigment remaining on the black paper have a problem in that they shine depending on the viewing angle and are visually recognized. This problem is solved by using the friction body 201 .

1: barrel 2: mounting hole 21: inward projection 21a: guide surface
21b Minimum inner diameter portion 3 Friction body 31 Inner hole 32 Friction portion 4 Large diameter portion 41 Annular surface 5 Mounting portion (small diameter portion)
51 Outward protrusion 51a Guide surface
51b Maximum outer diameter portion 52 Bulging portion 53 Downward extension portion 6 Annular space 7 Center core 71 Ventilating portion 72 Upper core portion 73 Lower core portion A Axial length from the upper end of the mounting portion to the upper end of the outward protrusion B Axial length from the upper end of the mounting hole to the lower end of the inward protrusion C Clearance between the inward protrusion and the outward protrusion

Claims (10)

A thermochromic writing instrument comprising a thermochromic ink and a friction body for thermally discoloring a mark written with the thermochromic ink by frictional heat,
The thermochromic ink contains a metallic luster pigment,
The thermochromic writing instrument is provided with a mounting hole for mounting the friction body,
the friction body includes a mounting portion that is inserted into the mounting hole, and a friction portion that has a convex curved surface shape and protrudes from the mounting hole,
a volume Ve of the friction portion and a volume Vp of the metallic luster pigment satisfy 5≦Ve/Vp≦35,
The maximum outer diameter D and the protruding length L of the friction portion satisfy 0.1≦L/D≦1.5,
The material of the friction body is a thermochromic writing instrument whose Shore A hardness immediately after the indenter starts to contact the material, as measured in accordance with JIS K 7215 of the Japanese Industrial Standards, is in the range of 60 to 85, and whose Shore A hardness (ΔHS) value defined by the following formula is 0 to less than 5.
ΔHS=(Shore A hardness value immediately after the indenter starts contacting)−(Shore A hardness value 15 seconds after the indenter starts contacting) The thermochromic writing instrument according to claim 1, wherein the material of the friction body has a product (Tb x Eb) of tensile strength at break Tb and elongation at break Eb, measured in accordance with JIS K 6251 of the Japanese Industrial Standards, of 5,000 or more and 18,000 or less. the mounting hole is provided to penetrate the rear end of the barrel or the top of the cap constituting the thermochromic writing instrument along a central axis in a vertical direction, and has an inner circumferential surface between two openings located at the upper end and the lower end;
An inward protrusion is formed on an inner circumferential surface of the mounting hole so as to protrude toward the inside of the mounting hole,
An outward protrusion is formed on an outer circumferential surface of the mounting portion so as to protrude outward from the mounting portion,
When the mounting portion is inserted into the mounting hole, the outward protrusion overcomes the inward protrusion, whereby the outward protrusion and the inward protrusion are engaged with each other,
The friction body has a straight inner hole extending along a longitudinal central axis and opening at least at a lower end of the mounting portion;
A rod-shaped core having a length that fits into the inner hole and an outer circumferential surface that contacts the inner circumferential surface of the inner hole is inserted into the inner hole,
A thermochromic writing instrument as described in claim 1 or 2, wherein when the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the core is held in a position corresponding to the inner surface of the mounting hole, so that the mounting portion is sandwiched between the outer surface of the core and the inward protrusion of the mounting hole. The thermochromic writing instrument according to claim 3, wherein when the attachment portion is inserted into the attachment hole and the core is inserted into the inner hole, the core has a length from the opening at the lower end of the inner hole to the opening at the upper end of the attachment hole. The thermochromic writing instrument according to claim 3 or 4, wherein when the attachment part is inserted into the attachment hole and the core is inserted into the inner hole, the lower end of the core is located at the same position as the lower end of the attachment part or higher than the lower end of the attachment part. The thermochromic writing implement according to any one of claims 3 to 5, wherein the inner hole is a hole that opens at the lower end of the attachment part and is closed at one end that does not open at the upper end of the friction part, and the core is provided with a ventilation part to exhaust air from within the inner hole during the process of inserting the core into the inner hole. The thermochromic writing instrument according to claim 6, wherein the ventilation section is a through hole that penetrates from one end of the core to the other along the vertical central axis of the core. The thermochromic writing instrument according to claim 6, wherein the ventilation portion is at least one groove or protrusion that continues from one end of the core to the other end along the outer circumferential surface of the core. The thermochromic writing instrument according to any one of claims 3 to 8, wherein the core has a vertically symmetrical shape. The thermochromic writing instrument according to any one of claims 3 to 9, in which a protrusion is provided on the outer circumferential surface of the core, the protrusion contacting the inner circumferential surface of the inner hole.

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